Thursday, June 16, 2011

ECG Interpretation Review #23 (Wide Tachycardia - WCT - VT vs SVT)

Is the rhythm below in Figure 1 sinus tachycardia? It was obtained from a hemodynamically stable man (BP=120/80 mmHg) with new-onset palpitations.
Figure 1 – Lead II rhythm strip from a patient with palpitations. BP = 120/80.
Is this sinus tachycardia? (Figure reproduced from ECG-2014-ePub )
- Note - Enlarge by clicking on Figures - Right-Click to open in a separate window.

INTERPRETATION:  The lead II rhythm strip shows a regular tachycardia at about 150/minute. Although the red arrow suggests sinus tachycardia – We are uncertain about QRS width, and therefore do not know how to proceed …
  • The “good news” – is that the patient is stable (BP=120/80). This means that there is time to confirm the diagnosis before beginning treatment.
  • The “less good” news – is that we do not yet know what the rhythm is …
The first steps (given that this patient is hemodynamically stable) – are to: i) obtain more history (History of underlying heart disease? of tachyarrhythmias such as documented SVT or VT? ) – and ii) obtain a 12-lead ECG during the tachycardia (being ready to cardiovert the patient if he at any time decompensates).
The 12-lead ECG during tachycardia is shown below (Figure 2):
Figure 2 – 12-lead ECG during tachycardia. Does this provide the answer?
(Figure reproduced from ECG-2014-ePub )
Note - Enlarge by clicking on Figures - Right-Click to open in a separate window. 
The 12-lead ECG obtained during tachycardia clearly reveals that the QRS complex is wide!
  • The small upright deflection in lead II (red arrow) is not a P wave after all.  Instead – the vertical red time lines show this deflection to be the initial part of the QRS complex! 
  • All other leads show the QRS to be very wide (>0.16 second).
  • The rate is about 150/minute.  The rhythm is regular. No P waves. 
IMPRESSION: This is a regular WCT (Wide Complex Tachycardia) with no sign of atrial activity. As emphasized in our KEY List below (Table 1) – always presume VT until proven otherwise! Statistically – the odds that a regular WCT without definite atrial activity is VT are at least 80%.  This goes up to over 90% if the patient also has underlying heart disease.
Table 1 – Common Causes of a Regular WCT without P waves.
(Figure reproduced from ECG-2014-ePub )
Note - Enlarge by clicking on Figures - Right-Click to open in a separate window.  
KEY Points in the Assessment of this Regular WCT:
  • VT  is by far the most common cause of a WCT when there is either no atrial activity or uncertain atrial activity. Although possible that a WCT may be due to supraventricular tachycardia with either preexisting bundle branch block or aberrant conduction – Always presume VT until proven otherwise. Treat accordingly.
  • Not all patients in VT immediately decompensate. Some may remain hemodynamically stable despite ongoing VT for hours, or even days …
  • Obtaining  a 12-lead tracing during tachycardia may be invaluable for honing in on the etiology of a tachycardia.  In this case, there are a number of clues that overwhelmingly suggest VT as the diagnosis.  These include: i) marked QRS widening in all other leads; ii) bizarre QRS axis during the tachycardia (extreme left axis deviation); iii) bizarre QRS morphology (not resembling any form of organized bundle branch block); iv) markedly negative QRS complex in left-sided lead V6 (which virtually always has more than a tiny r wave of positive activity); v) delayed R-to-S-nadir (VT very likely when there is an RS complex in any precordial lead with an interval from onset of the R until deepest point of the S >0.10 sec. - as it is in V5 and V6); and vi) concordance of the QRS in precordial leads (all precordial lead QRS complexes are predominantly negative). BOTTOM Line: “12 leads are better than one”and - a WCT without definite P waves should always be presumed to be VT until proven otherwise (regardless of whether or not the patient is hemodynamically stable).
- See Sections 08.0, 09.0 in our ACLS-2013-ePub -

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